PROJECT SUMMARY This project addresses fundamental mechanisms that contribute to the progression of acute brain injuries, including stroke and trauma. Our long-term goal is to develop interventions that can be applied at late time points, and which ultimately will be translatable to clinical studies to improve survival, and quality of life of survivors. The project focuses on the phenomenon of Spreading Depolarization (SD), which has recently emerged as a key contributor to the delayed progression of acute brain injuries. Recent clinical recordings now imply that repetitive SD waves cause progression of damage for many days in stroke and trauma patients. The challenge now is to understand how to block damaging SDs, or alternatively how to support injured brain tissue to survive deleterious effects of SD. This project therefore addresses key gaps in knowledge about mechanisms linking SD to injury. We will use brain slices and animal models to identify fundamental mechanisms that underlie damaging effects of SD, and approaches to support compromised tissues to recover from repeated SD episodes. Our central hypothesis is that agents that selectively reduce the duration of individual SD events will reduce episodic glutamate and Ca2+-mediated neuronal injury that occurs episodically with each SD event. Furthermore, preserving the propagation of SDs through peri-infarct tissues will maintain beneficial effects of SD required for brain recovery. We will test whether limiting glutamate transients and/or activation of NMDA-type glutamate receptors specifically during the late phase of SD will support neuronal recovery after SD. Specific Aim 1 tests the hypothesis that pathophysiological glutamate pulses are strictly limited to SD, and extended in metabolic compromised tissues, due to presynaptic release and disruption of astrocytic regulation in metabolically compromised slices. Specific Aim 2 tests the hypothesis that targeting the vulnerable phase of SD will promote neuronal recovery metabolically compromised tissues. Neuronal Ca2+ loading will be evaluated, and pharmacological interventions used to identify approaches to improve recovery of Ca2+ loading, without impairing beneficial mechanisms. Specific Aim 3 makes key tests of these mechanisms in an in vivo setting. Combined imaging and electrophysiological methods will be used throughout each aim, with cellular mechanisms characterized in brain slices (Aims 1&2) and then tested in vivo (Aim 3). Genetically- encoded sensors for glutamate and calcium will complement other single-neuron electrophysiological and imaging approaches. Pharmacological approaches will be will be tested to identify mechanisms and interventions that reduce deleterious effects of SD in metabolically compromised tissues. Successful completion of these aims should identify fundamental mechanisms linking SD to cellular injury in compromised tissues, and provide the basis for rational approaches that can be developed for interventions applied in the critical days following a range of acute brain injuries.